Fix nullref when getting struct from feature collection and it isn't present (#47795)

Author: BrennanConroy

src/Extensions/Features/src/FeatureCollection.cs

@@ -117,6 +117,17 @@ public IEnumerator<KeyValuePair<Type, object>> GetEnumerator()
     /// <inheritdoc />
     public TFeature? Get<TFeature>()
     {
+        if (typeof(TFeature).IsValueType)
+        {
+            var feature = this[typeof(TFeature)];
+            if (feature is null && Nullable.GetUnderlyingType(typeof(TFeature)) is null)
+            {
+                throw new InvalidOperationException(
+                    $"{typeof(TFeature).FullName} does not exist in the feature collection " +
+                    $"and because it is a struct the method can't return null. Use 'featureCollection[typeof({typeof(TFeature).FullName})] is not null' to check if the feature exists.");
+            }
+            return (TFeature?)feature;
+        }
         return (TFeature?)this[typeof(TFeature)];
     }
 

src/Extensions/Features/test/FeatureCollectionTests.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Http.Features;
@@ -44,4 +45,62 @@ public void SetNullValueRemoves()
         var thing2 = interfaces[typeof(IThing)];
         Assert.Null(thing2);
     }
+
+    [Fact]
+    public void GetMissingStructFeatureThrows()
+    {
+        var interfaces = new FeatureCollection();
+
+        // Regression test: Used to throw NullReferenceException because it tried to unbox a null object to a struct
+        var ex = Assert.Throws<InvalidOperationException>(() => interfaces.Get<int>());
+        Assert.Equal("System.Int32 does not exist in the feature collection and because it is a struct the method can't return null. Use 'featureCollection[typeof(System.Int32)] is not null' to check if the feature exists.", ex.Message);
+    }
+
+    [Fact]
+    public void GetMissingFeatureReturnsNull()
+    {
+        var interfaces = new FeatureCollection();
+
+        Assert.Null(interfaces.Get<Thing>());
+    }
+
+    [Fact]
+    public void GetStructFeature()
+    {
+        var interfaces = new FeatureCollection();
+        var value = 20;
+        interfaces.Set(value);
+
+        Assert.Equal(value, interfaces.Get<int>());
+    }
+
+    [Fact]
+    public void GetNullableStructFeatureWhenSetWithNonNullableStruct()
+    {
+        var interfaces = new FeatureCollection();
+        var value = 20;
+        interfaces.Set(value);
+
+        Assert.Null(interfaces.Get<int?>());
+    }
+
+    [Fact]
+    public void GetNullableStructFeatureWhenSetWithNullableStruct()
+    {
+        var interfaces = new FeatureCollection();
+        var value = 20;
+        interfaces.Set<int?>(value);
+
+        Assert.Equal(value, interfaces.Get<int?>());
+    }
+
+    [Fact]
+    public void GetFeature()
+    {
+        var interfaces = new FeatureCollection();
+        var thing = new Thing();
+        interfaces.Set(thing);
+
+        Assert.Equal(thing, interfaces.Get<Thing>());
+    }
 }